How to pee without splashback, or how fluid dynamics might save your marriage

To you and I, it’s called splashback — for physicists Tadd Truscott and Randy Hurd of the Brigham Young University Splash Lab, though, it’s called urinal dynamics. I am of course talking about the nasty habit of urine splashing out of a urinal or toilet and onto the floor — or worse, the urinator himself. Truscott and Hurd have spent the last few months analyzing the male urine stream, and with a bit of applied fluid dynamics — and a healthy dollop of high-speed camera footage (embedded below) — they think they’ve finally worked out how to pee without creating splashback. They’re so confident that they’re going to present their findings to the American Physical Society.

Their urinal dynamics research provided some interesting findings — though they’re not entirely unexpected if you’re an enlightened male. Pee splashback is caused by two main factors: height from the toilet/urinal bowl, and the “angle of attack.” By far the best way to reduce splashback is to alter the angle of your pee stream so that it hits the wall of the toilet/urinal at a gradual angle; the closer to 90 degrees, the worse the splashback will be. The other easy way of saving your marriage is by simply sitting down: Your pee travels five times farther when you’re standing up, picking up a lot of velocity on the way, creating far more splashback. Sitting down usually implies a narrower angle of attack, too.

Other ways of reducing splashback include not peeing directly into the water, and laying down an shock-absorbing layer of toilet paper before you begin. As you can see in the (strangely mystifying) video below, peeing into a body of water creates a cavity that then collapses in on itself, creating massive splashback. The physicists also note that various materials, baffles, and other obstacles (urinal cakes) can all make a big difference. Porcelain, for example, is hydrophilic, causing urine to form puddles, which then cause splashback when hit by more urine. Hybrophobic surfaces, such as on your car’s windshield or smartphone screen, would reduce splashback a lot.

As you can probably imagine, for a variety of reasons — hygiene, ethics, controlling for environmental factors, repeatability… — the Splash Lab didn’t use “in the field” testing. Rather, the researchers built some special apparatus (pictured right) that simulates male urination, including the Plateau-Rayleigh instability that causes your pee stream to break up into droplets (also increasing splashback, incidentally — the deck is definitely stacked against us men). They then filled the apparatus with colored water, set up a high-speed camera, and systematically synthetically urinated on a variety of different targets.

While this might all sound like fun and a waste of university funds, the Splash Lab’s research into urinal dynamics is actually a serious endeavor. The simple matter of the fact is that splashback is unhygienic. Splashback, and the bacteria that breeds in the puddles of pee, is one of the reasons that public bathrooms smell so bad. In hospitals, nursing homes, and other large institutions, splashback can be a serious health risk. The Splash Lab hopes that its research will help with the development of better toilet designs and usage habits that minimize pee splashback, thus increasing health and reducing matrimonial stress worldwide.